Conventionally, there is proposed an active vibration noise control device for controlling an engine noise heard in a vehicle interior by a controlled sound output from a speaker so as to decrease the engine noise at a position of passenger's ear. For example, noticing that a vibration noise in a vehicle interior is generated in synchronization with a revolution of an output axis of an engine, there is proposed a technique for canceling the noise in the vehicle interior on the basis of the revolution of the output axis of the engine by using an adaptive notch filter so that the vehicle interior becomes silent.
By the way, in a narrow vehicle interior environment, there is a case that a deep dip of transfer characteristics from a speaker to a microphone occurs due to a sound wave interference and a reflection in a vehicle interior space. In such a frequency band that the deep dip occurs, an operation of the adaptive notch filter tends to become unstable, and a noise-canceling effect tends to decrease.
For example, in Patent References 1 and 2, there is proposed a technique for solving the above problem. In Patent Reference-1, there is proposed a technique for increasing a gain applied to transfer characteristics. In Patent Reference-2, there is proposed a technique for using multiple speakers, and for switching a speaker to be used in accordance with a noise frequency. Concretely, the technique verifies transfer characteristics of paths related to the multiple speakers, and selects a path of speaker in which an influence of the dip is small (in other words, a speaker to which the largest gain is applied).